1. Field of the Preferred Embodiment(s)
This invention generally relates to resistors for electronics. Specifically, the invention is a group of impedance matching or terminating resistors mounted in a high density network or array package using spherical solder connections and having low noise characteristics.
2. Description of the Related Art
Resistor networks are commonly used to terminate high speed digital signal lines to minimize unwanted reflections back through the transmission structure which is typically a printed circuit board. In most applications, the terminations are made by placing a resistor with a resistance matching the impedance of the transmission line, at the end of the transmission line. One end of the resistor is connected to a common termination voltage and the other end is connected to the signal line. For these applications a bussed resistor network is a convenient solution, since one end of the termination is common to all signal lines.
The previous resistor network designs including surface mount, SIP and DIP versions have had resistors and conductor arrangements with individual conductor lines running for a length of some distance on the network before being tied to a common point. This is necessitated because all the external off resistor network connections are made at the periphery of the device and a conductor must be run from the periphery of the device to the individual resistor. The lengthy line length causes each resistor/conductor pair to have a higher mutual inductance between adjoining resistor/conductor pairs and leads to significant cross-talk noise being coupled between the resistor/conductor pairs when the resistor network is employed in its typical use as a terminating or impedance matching resistor for simultaneously switching transistors in an electronic device. As the transistor density and speed of semiconductor devices increase, the problem of cross-talk noise causing an erroneous signal becomes more of a problem in all areas of the electronic package and must be taken into consideration when designing electronic packaging. Further, at high frequencies, the high inductance of the common termination lines can cause a high impedance to appear at the end of the transmission line.
Despite the advantages of each type of prior art resistor network, none have been easily or economically manufactured with a high density of interconnects per unit area on a printed circuit board. In particular, providing the electrical connections only on the periphery of the resistor network causes the electrical leads to be tightly spaced on the edge of the device, while the area in the interior of the device is unused for electrical interconnections.
Therefore, there is a current unmet and heretofore long felt need for a resistor network with higher density, low cross-talk noise and improved signal integrity.